Artificial reverberations are often used for dry audio contents to simulate effects of real environments. In many applications such as headphone and speaker playbacks, artificial reverberations are added to give the listeners a sense of being in the real environments.
In nature, reverberations are echoes from various reflections in real environments, such as a room. The ideal way of generating reverberations will be convolving the audio signal with the impulse response of the desired environment. Such a method in practice is computationally costly. In a digital signal processing application, it takes huge computational and storage resources to implement this method. To reduce the cost, for example, conventional methods provide an electronic sound processor for creating reverberation effect by convolving random white noise with dry audio signals to simulate the late part of the reverberation.
A number of conventional methods approximate the exact reverberation or to create only the salient signals. Most of the algorithms use feedback loops with delay lines, sometimes combined with allpass filters. For example, in one conventional system, an electric reverberation apparatus includes a plurality of loops having different delay times and adapted to form sound repetitions of diminishing intensity. The loops are typically provided with tappings, each of which has a particular delay time associated with it.
A conventional reverberation effect imparting system includes a number of comb filters, each of which has a signal delay line and a feedback loop for filtering a delayed output signal from the delay line and feeding the filtered signal back to the input side with a variable loop gain. The drawback of such feedback systems is that they will create resonates thus colorizes the sound. These problems may be overcome by phase-shifting or time-variant delay lines in some algorithms, which introduce certain undesired pitch shifting effects.
Other conventional systems use only delay lines and feed forward loops, tapping at different locations of the delay lines. Still other conventional systems use algorithms that separate the reverberations to early and later parts and generate them separately. This typically leads to a sudden increase of echo density at the boundary, which is not true in a natural environment.
There is therefore a need for improved reverberation devices.